Fluid lines bearing pressurized fluid (“pressure fluid lines”) often do not have any type of automatic leak detection system, and only manually actuated shutoff valves are available on the lines should a leak be detected for any reason. For example, in a typical residence, there may be as many as sixteen such lines serving fixtures and appliances such as toilets, sinks, clothes washers, etc. If a line or fitting leaks for any reason, typically the only knowledge of the leak comes from direct human observation of the water or damage caused by the water, as opposed to any form of automatic sensor.
Automatic leak detection systems and electrically controlled shutoff valve systems do exist, but they are typically too expensive for residential housing and similar situations. In many cases, they require that the detection system be electrically powered at all times. This is undesirable, because power outages do occur, and can in fact be the cause of the leakage. For example, a power outage in the late fall or early spring can cause an unoccupied summer residence to cool down so much that a water pipe, yet to be drained for the winter, bursts due to freezing water. Such systems also typically employ a spring-driven normally open valve so that the fixture or appliance downstream of the valve will still operate if the power or other portions of the system fail, but there is obviously no leak present and the fixture must be operated normally anyway. A normally closed valve system would fail closed and shutoff fluid to the appliance even though no leak had been detected.
Another problem faced by such systems is sediment buildup in the valve. Even the most clean of domestic water systems has some sediment level, and especially in rural areas sediment is present in well water. It may be many years before a leak occurs, but the valve must work properly the first time it is activated by the leak detection system.